java - 我的微调器在添加从 firebase 数据库中选择的多个值时被覆盖

Question

我想从 courseName 中获取所有值并用它来填充微调器:

databaseReference.addChildEventListener(new ChildEventListener() {
  @Override
  public void onChildAdded(DataSnapshot dataSnapshot, String s) {
    final List<String> courses = new ArrayList<String>();
    for (DataSnapshot courseSnapshot: dataSnapshot.getChildren())
    {
      String courseName = courseSnapshot.getValue(String.class);
      courses.add(courseName);
    }

    Spinner spinnerCourse = findViewById(R.id.spinnerCourse);
    ArrayAdapter<String> courseAdapter = new ArrayAdapter<String>(AddSubject.this,android.R.layout.simple_spinner_item, courses);

    courseAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinnerCourse.setAdapter(courseAdapter);
  }
}

Answer 1

你需要先清除你的列表，然后使用 clear() 方法绑定(bind)它

    databaseReference.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) 
    {
      final List<String> courses = new ArrayList<String>();
      courses.clear();
      for (DataSnapshot courseSnapshot: dataSnapshot.getChildren()) 
      {
          String courseName = courseSnapshot.getValue(String.class);
          courses.add(courseName);
      }
      Spinner spinnerCourse = findViewById(R.id.spinnerCourse);
      ArrayAdapter<String> courseAdapter = new ArrayAdapter<String>(AddSubject.this,android.R.layout.simple_spinner_item, courses);
      courseAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
      spinnerCourse.setAdapter(courseAdapter);
    } 
   }